(Reuters) — MetLife Inc. said it would file a lawsuit Tuesday against regulators subjecting it to tougher oversight, challenging their verdict that the firm harbors enough risk to bring down the financial system in a crisis.

The company, the largest U.S. insurer, unsuccessfully contested the decision by the Financial Stability Oversight Council in a hearing last month, and a lawsuit was its last resort to escape being overseen by the Federal Reserve.

The designation of MetLife as a so-called "systemically important" company would make insurance products more expensive without actually enhancing financial stability, it said.

"FSOC's designation of MetLife is premature," MetLife's head, Steve Kandarian, was quoted as saying in a statement. "The council should wait until the rules are in place and it knows the impact on designated firms."

The remark was a reference to the U.S. Federal Reserve, which has yet to come up with capital rules for insurers. The industry is often skeptical that the central bank, which has long overseen banking, knows enough about insurance.

The 2010 Dodd-Frank Wall Street Reform and Consumer Protection Act passed after the 2008-2009 financial crisis put more onerous regulatory demands on the largest banks and also authorized the FSOC to subject other large and risky firms such as insurers to a similar regime.

American International Group Inc., which almost collapsed during the credit meltdown, is now overseen by the Fed, as is Prudential Financial Inc. Including MetLife, the Fed oversees almost one-third of the entire industry in America, a study showed last year.

MetLife said it had filed its lawsuit in the U.S. District Court for the District of Columbia. It had hired Gibson, Dunn & Crutcher L.L.P. and Sullivan & Cromwell L.L.P. as its law firms.

Eugene Scalia, a lawyer at Gibson Dunn, is on MetLife's team to help it with the lawsuit. The son of Supreme Court Justice Antonin Scalia, he has a track record of successfully fighting decisions by federal regulators.